Progress of the interaction between e - and molecule in Fudan University

Transcription

1 Progress of the interaction between e - and molecule in Fudan University B. Wei, Z. Chen, X. Wang, R. Hutton, Y. Zou Fudan University, Shanghai The 2nd Research Coordination Meeting (RCM) of the CRP, May 2011, IAEA, Vienna

2 Outline Introduction of the recoil-ion and electron momentum spectroscopy at Fudan University The testing experiment between the ns Laser pulse and supper-sonic gas The pulse low energy electron beam and the interaction of e - -molecule Summery and Outlook

3 Work Plan for this CRP at Fudan University 1. Construct a low energy pulse electron beam and Combine it with the collision system 2. Study the electron impact ionization and dissociation process for H 2 and C n H m 3. Study the interaction of the electron and N 2 and O 2

4 Electron ionization of Methane ---D. Reiter, R. K. Janev, Contrib. Plasma Phys., 50 (2010) 986

5 Electron ionization of Methane CH 4 2 CH 3 H CH 4 CH 3 H ---D. Price, et al, J. Chem. Phys. 134, , 2011

6 Recoil-ion and electron momentum spectroscopy (RIMS) Position Sensitive Multi-hit Electron Detector Position Sensitive Multi-hit Ion Detector Electrons Recoil Ions RIMS Time of Flight & 2dim positions 3 dim momentum vectors The first recoil-ion momentum measurements were undertaken by Ullrich and Schmidt-Böcking in Frankfurt

7 Principle of momentum image a d ion trajectory U -U TOF ( E) f m E 2a qu E E d qu time in ns, m in amu, E and qu in ev, distance in cm f = 720

8 Ion Kinetic Energies for Electron Impact Ionization of CH 4 T. D. Märk et al, Int. J. Mass Spectrometry, 228 (2003) 307 For a helium gas at room temperature: P = 5.9 a.u. (65 mev) Final state energy of electron extend from milli ev to ev, Recoil ions from micro ev to milli ev (atoms), or 10 ev (molecules)

9 Trajectories of the recoil ions in TOF K E = 0.4 ev K E = 0.2 ev E = 4 V/cm E = 4 V/cm The trajectories correspond to a recoil ion with an initial velocity direction θ increasing from -90 o to 90 o by a step of 10 o.

10 Detector and Data Acquisition System V1290N, is a high performance Multi-hit TDC provided by CERN. The double hit resolution is 5 ns, 52 us full scale range and 21 bit resolution. A 6U VME bus embedded computer VP9 used here to control the DAQ, the software development for the DAQ based on UnisDX-XP the total time resolution for the system better than 1 ns and the dead time is shorter than 10 ns. The DAQ system can reach a data transfer rate of 160 Mb/s. --- Nuclear Science and Technique, 20 (2009) 51-55

11 Supersonic Gas-jet gas in Gas-jet P 0 Pump 1 P 1 Skimmer 1 P 2 Skimmer 2 Pump 2 P 3 Skimmer 3 Pump 3 P 4 P 5 P 6 Pump 6 stage Diameter Pump 4 (mm) Turbomolecular pumps (l/s) Background Vacuum (Torr) Vacuum (3 bar gas injection) Pump

12 Interaction between ns Laser pulse and supper-sonic gas Amp.& Discr. start Recoil ion detector Gas-jet common stop D A Q Counts Lens f = 100 mm H H 2 C 2 Diode Discr Time of Flight (us) C CH3 CH CH2 Counts/arbitrary units H CH 3 H 2 CH Time of Flight (us) C

13 Interaction between ns Laser pulse and Methane Counts H I E = 12.6 ev, hv = 2.33 ev Binding energy of the CH 3 H bond is 1.3 ev. C CH3 CH CH2 0.4 H 2 C Time of Flight (us) --- Z Chen, X Wang, B Wei, et al, Phys. Scr. T144 (2011)

14 Interaction between ns Laser pulse and Methane H H 2 6 mj CH C CH 3 CH 2 13 mj 24 mj 86 mj C

15 Average Kinetic energy as function of Laser intensity kinetic energy related to ion s velocity in TOF direction

16 Low Energy Electron Gun Electron Energy: 1~2000 ev Energy spread : 0.4 ev Current: 1nA ~ 10 μa ELG-2 / EGPS-1022, Kimball Physics

17 Ultra Fast Pulse Generator 0.5 ns 1 ns Frequency up to 100 khz

18 Testing of electron gun: Beam current as a function of the electron energy Electron beam passes through a 1 mm Molybdenum aperture, and collected by a Faraday Cup. Frequency: 50 khz Pulse width: 1 ns

19 Experimental setup e - detector Farady cup Slit e - gun E Gas Recoil ions detector Pressure in Collision Chamber: 3.0 X 10-9 Torr Strength of the extraction field in TOF: 4 V/cm

20 Interactions between Electron and Supper-sonic Gas (Ar) ev e-ar FWHM(Ar ): 160ns FWHM(Ar 2 ): 143ns Ar H Ar 3 2 Ar H 36 Ar 2 O N 2 O tof/100ns

21 Interaction between electrons and CH 4 molecule eV CH 4 Counts FWHM(CH 4 ): 134ns FWHM(CH 3 ): 340ns CH H 13 CH 4 H Time of Flight (100ns)

22 The dissociation of the methane ions TOF ( E) f m E 2a qu E E d qu CH 3

23 Modification of the TOF system The transverse extraction field is suitable for the highly charged ion beam and laser beam. However, the electron beam can not perpendicularly penetrate the magnetic field. e - detector e - gun Slit Gas E Recoil ions detector Farady cup Using a longitudinal extraction field, the incident electrons has the same direction with the magnetic field.

24 Titanium Chamber for the interaction of the low energy electrons and molecules No residual magnetic: Ti High Vacuum: Torr longitudinal extraction field

25 Summery and Outlook The low energy pulse electron beam source has been tested and combined with the RIMS. By measuring the interaction between low energy electron and molecule (CH 4 ), the collision system has been tested. A full-titanium collision chamber is being manufactured. The designed vacuum is better than 3X10-10 Torr. Future measurements will aim at cross-sections for ionization and dissociation of molecules (C x H y,n 2 ) by electron impact.

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